Hard disk drives are used in many computer system operations. In fact, many computing systems operate with some type of hard disk drive to store the most basic computing information, e.g., the boot operation, the operating system, the applications, etc. In general, the hard disk drive is a device, which may or may not be removable, but without which, some computing systems may not operate.
One basic hard disk drive model was developed approximately 40 years ago and in some ways resembles a phonograph type apparatus. For instance, the hard drive model includes a storage disk or hard disk that spins at a standard rotational speed. An actuator arm or slider is utilized to reach out over the disk. The arm has a magnetic read/write transducer or head for reading/writing information to or from a location on the disk. The complete assembly, e.g., the arm and head, is called a head gimbal assembly (HGA). The assembly consisting of the disks, HGAs, spindle, housing, and the other parts internal to the housing is called the Head Disk Assembly, or HDA.
In operation, the hard disk is rotated at a set speed via a spindle motor assembly having a central drive hub. Additionally, there are channels or tracks spaced at known intervals across the disk. Most current embodiments arrange the signal regions in concentric circular tracks, but other designs, such as spirals or irregular closed or open paths are possible and useful. When a request for a read of a specific portion or track is received, the hard disk aligns the head, via the arm, over the specific track location and the head reads the information from the disk. In the same manner, when a request for a write of a specific portion or track is received, the hard disk aligns the head, via the arm, over the specific track location and the head writes the information to the disk. Refinement of the disk and the head have provided reductions in the size of the hard disk drive. For example, the original hard disk drive had a disk diameter of 24 inches. Modern hard disk drives are much smaller and include disk diameters of less than 2.5 inches. Small disk drive type apparatus such as micro drives can be smaller still. Refinements also include the use of smaller components and laser and other optical related components within the head portion. Reducing the read/write tolerances of the head portion allows the tracks on the disk to be reduced in size by a corresponding margin. Thus, as modern laser and other electro-optical and other micro recognition technologies are applied to the head, the track size on the disk can be further compressed.
The ever increasing need for data storage has led some disc drive makers to steadily increase the amount of data stored on a drive. Mechanical considerations, radiated audible noise limits, power requirements, and other factors limit the number of discs that can be economically combined in a single drive. Thus, disc drive technology has generally focused on increasing the amount of data stored on each disc surface.
Typically, tracks are arranged concentrically about a disk's surface or in an analogous arrangement. One method of increasing the amount of data a disk can store is to make each data track narrower, which allows the tracks to be spaced more closely together. This allows a larger number of tracks on each disk surface. But, as tracks become narrower, signals generated in the head caused by media alterations (e.g., from data written to the disk's magnetic, optical, thermal, and/or other media) become more difficult to detect. Thus, the signal to noise ratio can worsen, particularly in the presence of electronic and media-induced signal degradation and noise. One method to improve the signal to noise ratio, and hence the detection of media alteration (e.g., “writing”), is to position the heads more closely to the media surface. This causes the media alteration-sensing components of the head to be physically closer to the media alterations, thus improving the head sensor's ability to detect the media alterations comprising the written signal. However, care must be taken to avoid unintended contact between the head components and the moving media surface.
Typically, the heads are lightly spring loaded, with the spring tension perpendicular to the media surface plane and directed against the media surface. An air bearing separates the head and media surfaces as follows: As the media moves relative to the head, air is dragged by the disc surface through specifically designed channels in the surface of the head adjacent to the media surface. The surface of the head and the channels contained therein, collectively referred to as the air-bearing surface (ABS), are designed to generate a regions of increased air pressure in between the ABS and media surface that forces the head away from direct contact with the media surface, in effect causing the head to fly above the media surface. The separation of the head ABS and media surface, commonly called fly height, is a complex phenomenon primarily a function of air density, the spring preload, the relative speed between the head and media surface, and the pattern of channels present on the head air bearing surface adjacent to the media surface.
It is well known to those familiar with head-disk interface design that a particular head-disk combination will not fly precisely at the desired separation. Variances in mechanical tolerances, spring tensions, and other factors result in a nearly normal statistical fly-height population distribution generally centered about the mean fly height. Furthermore, the head and its mounting gimbal are subject to mechanical tolerances, aerodynamic forces, and inertial forces that can cause it to deviate from the desired attitude with respect to the media surface, e.g. static and dynamic pitch and roll). This can move some areas of the air bearing surface closer or further from the media surface.
Reducing the fly-height, while increasing the signal-to-noise ratio of the recovered signal, can lead to reduced disc drive reliability. Such reliability reduction can occur in the presence of particulate contamination. Particulate contamination can include wear particles from drive components and/or airborne contaminates from the ambient surroundings. Such particulate contaminants can accumulate on the air bearing surface.
This buildup of contaminants can disrupt air flow, thus causing the head to fly higher or lower than desired, or at a different orientation relative to the media surface than desired. This results in an increase in the width of the head design's fly height distribution, as indicated by a higher fly height population standard deviation, referred to as “sigma”. A higher fly height sigma necessitates a higher targeted average fly height, to ensure an acceptable portion of head population will operate at greater than the minimum allowed fly height. Higher average fly height can cause reduced average transducer performance (e.g., signal to noise ratio) and/or lower areal densities.
The particulate buildup can also bridge the narrow fly height gap. This can lead to fouling and contact between the head and media. The resulting friction can generate more particles, which can further exacerbate contamination. This can lead to drive failure. Drive failure can occur rapidly by this mode.
The particulate buildup may also collect near the transducer elements. Much of the drive wear products have significant ferromagnetic properties. Thus, the magnetic sensitivity of a drive read element can be distorted and reduced, which can lead to lowered signal to noise ratios and drive failure. In an optical drive, contaminants can distort and/or occlude the optical path, which can result in poor performance.